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They are, he says, an "invitation" to those who see "beauty" to dive into the world of intelligence gathering.

The GCSB is New Zealand's "signals intelligence" spy agency - our nation's "electronic eavesdropping" contribution to the Five Eyes network which also consists of Australia, Canada, the United Kingdom and the United States.

Other partner agencies have used similar recruiting exploits. In the United Kingdom, the Government Communications Headquarters launched its first puzzle challenge in 2011, saying: "Decoding plays a direct role in predicting and thwarting major attacks."

Like its offshore counterparts, the bureau and its sibling agency, the NZ Security Intelligence Service, were forced out into the light after whistleblower Edward Snowden's disclosures in 2012 demanded greater accountability and openness.

A report published in 2013 revealed the bureau had become estranged from its legal baseline and healthy public sector good practice.

The GCSB, which also has responsibility for New Zealand's cyber protection, has undergone a massive overhaul since.

In that time, both the GCSB and NZSIS have received huge funding boosts - and gone a huge recruiting drive. Part of that recruitment exercise has been to improve diversity at a place previously seen as very male and mostly Pakeha.

GCSB director-general Andrew Hampton said: "To put it simply, our mission is to protect New Zealand and New Zealanders."

Bletchley Park in England, where Alan Turing led a team of code breakers who defeated Germany's Enigma cryptography machine to help with World War II.

He said the bureau needed a diverse workforce which was strong in science, technology, engineering and maths.

The drive towards diversity reflected the positions taken by Five Eyes' partners - a former GCHQ director said "dull uniformity would completely destroy us".

Hampton said reflection on the GCSB workforce in 2016 found "room for improvement".

It had since reduced a gender pay gap of greater than 10 per cent - skewed against women - to 5 per cent. The bureau also now offered scholarships to women wanting to study in areas it considered critical.

While slightly more than half of senior leaders were now female, its overall staff was only about a third women.

In the technical trades of science, technology, engineering and maths, just 16.5 per cent of staff were female.

"This lack of females in technical roles is unacceptable and a barrier to us fully addressing our gender pay gap," Hampton said.

While statistics showed men traditionally dominated the numbers of those working in those fields, he said there were a number of innovations to redress the balance.

The scholarship programme had also raised the profile of the GCSB as a potential employer among women. Of 300 recent applications from graduates, 124 were from women. There were eight jobs going - women got five. Just two years ago, only 14 per cent of applications were from women and none were hired.

Last week, the States Services Commission issued its latest "health check" on the intelligence agencies through its Performance Improvement Framework system. The reports benchmark government agencies and challenge improvement.